Capacitance fuze

ABSTRACT

1. A proximity fuze comprising: A. A FIRST CONDUCTING BODY AND A SECOND CONDUCTING BODY, SAID FIRST CONDUCTING BODY SEPARATED FROM SAID SECOND CONDUCTING BODY, SAID FIRST AND SECOND CONDUCTING BODIES LYING SUBSTANTIALLY IN AN EDGEWISE RELATION ON THE OUTER SURFACE OF A PROJECTILE, B. A SOURCE OF DIRECT CURRENT POTENTIAL CONNECTED BETWEEN SAID FIRST CONDUCTING BODY AND SAID SECOND CONDUCTING BODY, SAID SOURCE OF DIRECT CURRENT POTENTIAL ESTABLISHING AN ELECTRIC FIELD BETWEEN SAID BODIES WITH A POSITIVE CHARGE ON SAID FIRST CONDUCTING BODY AND A NEGATIVE CHARGE ON SAID SECOND CONDUCTING BODY, SAID ELECTRIC FIELD EXTENDING INTO THE MEDIUM SURROUNDING SAID CONDUCTING BODIES, AND SAID PROJECTILE, C. DETONATING CIRCUIT MEANS INCLUDING VACUUM TUBE MEANS HAVING AN ANODE, A CATHODE, AND A GRID, SAID FIRST CONDUCTING BODY CONNECTED TO SAID GRID, AND SAID SECOND CONDUCTING BODY CONNECTED TO SAID CATHODE, SAID DETONATING CIRCUIT MEANS BEING RESPONSIVE TO A TIME RATE OF CHANGE IN THE CHARGE ON SAID BODIES RESULTING FROM A CHANGE IN THE ELECTRIC FIELD CONFIGURATION SURROUNDING SAID CONDUCTING BODIES AND SAID PROJECTILE.

United States Patent [191 Krupen May 13, 1975 CAPACITANCE FUZE [75]Inventor: Philip Krupen, Silver Spring, Md.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

22 Filed: Nov. 14, 1962 21 Appl. No.: 237,764

[52] U.S. Cl. l02/70.2 P [51] Int. Cl. F42c 13/00 [58] Field of Search102/702, 70.2 P, 18, 19.2,

[56] References Cited UNITED STATES PATENTS 2,998,775 9/1961 Craft102/702 R 3,001,476 9/1961 Boykin 102/702 R Primary Exanziner-BenjaminA. Borchelt Assistant ExaminerC. T. Jordan Attorney, Agent, orFirmNathan Edelberg; Robert P. Gibson; Saul Elbaum EXEMPLARY CLAIM l. Aproximity fuze comprising:

a. a first conducting body and a second conducting body, said firstconducting body separated from said second conducting body, said firstand second conducting bodies lying substantially in an edgewise relationon the outer surface of a projectile,

b. a source of direct current potential connected between said firstconducting body and said second conducting body, said source of directcurrent potential establishing an electric field between said bodieswith a positive charge on said first conducting body and a negativecharge on said second conducting body, said electric field extendinginto the medium surrounding said conducting bodies, and said projectile,

c. detonating circuit means including vacuum tube means having an anode,a cathode, and a grid, said first conducting body connected to saidgrid, and said second conducting body connected to said cathode, saiddetonating circuit means being responsive to a time rate of change inthe charge on said bodies resulting from a change in the electric fieldconfiguration surrounding said conducting bodies and said projectile.

1 Claim, 2 Drawing Figures PATENTED MAY 1 31975 DE-TONATOR /w l I //VVENTOE DETONATOR 56 PH/z/P Ker/PEN CAPACITANCE FUZE The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment to me of any royalty thereon.

This invention relates to proximity fuzes, and more particularly to anon-radiating capacitance fuze.

In firing an explosive projectile at a target it is difficult to timethe explosion so that it will occur at the most advantageous positionwith respect to the target.

Military munitions, such as bombs and mortar shells which are used ingreat quantities, rely on proximity fuzes to cause detonations that havea maximum destructive effect.

Proximity fuzes may be broadly classified either as radio systems or asnon-radio system. The normal radio system ultimately depends on thereceipt of a radio signal for detonation. Such systems, while highlydeveloped, tend to be complicated and expensive. Also they requireextensive protective circuitry in order to be relatively immune fromenemy jamming. Non-radio systems are, in general, simple, inexpensive,and inherently less susceptible to enemy jamming. Non-radio systems,however, which use A.C. circuitry in their detection operation radiateelectromagnetic energy, providing an opening through which enemy jammingcan operate.

It is an object of this invention to provide a novel compact, lightweight, low cost fuze.

Another object of the invention is to provide a nonradiating proximityfuze.

A further object of this invention is to provide a direct currentoperated detection device for a fuze.

A still further object of this invention is to provide a novelnon-radiating fuze which is relatively insensitive to weatherconditions.

The invention, deceptive in its simplicity, consists in its elementalform merely of two conducting bodies separated by a dielectric medium, asource of direct potential, and a resistance connected in series. Aswill be more fully developed later in the specification, current flowthrough the resistor generates the detonating voltage when the capacitybetween the conducting bodies changes due to an onrushing target.

As is well known, two conducting bodies forming a capacitor have whatmay be termed a fringe effect, that is, the electrostatic field betweenthe two conducting bodies which form the capacitor will bulge out alongthe edges. Any change in the dielectric constant of the material in thisfringe field will result in a change in the effective capacitancebetween the conducting bodies. It is a target causing a change in thedielectric constant of the fringe field, which is used in accordancewith the teaching of this invention, to produce a firing signal.

The specific nature of the invention, as well as other objects, uses andadvantages thereof, will clearly appear from the following descriptionand from the accompanying drawings in which:

FIG. 1 is a simplified schematic drawing of a fuze embodying theprinciples of this invention.

FIG. 2 is a schematic drawing of a specific embodiment of the invention.

Referring to FIG. 1, there is shown one embodiment of the simple, directcurrent operated, non-radiating fuze of this invention. The fuzeconsists principally of two conducting bodies 11 and 12 separated by adielectric medium, with a source of potential 13 and a resistor 14connected between them. A detonator or detonating circuit 15 shown inblock diagram form, is connected across resistor 14. The detonatingsignal is developed in the resistor 14.

The operation of the fuze illustrated in FIG. 1 may be analyzed asfollows. Equilibrium is established before the fuze approaches a target16 so that a potential difference V, equal to the source potential 13,exists between the conducting bodies 11 and 12 across an effectivecapacitance C which exists between them. At equilibrium there is nocurrent flow in the resistor 14 and the circuit is governed by theequation;

Q=VC

where Q is the charge on the bodies 11 and 12, V is the source voltage13, and C is the total capacitance between the bodies 11 and 12including the capacitance due to the fringe field. As the munitionapproaches a target 16 the capacitance C, between the bodies 11 and 12increases due'to a change in the fringe field caused by the entry of thetarget. The equation governing the circuit in this case is;

where, AC is the change in capacitance due to the change in the fringefield," and AQ is the resultant change in charge. To maintainequilibrium the charge AQ flows through the resistance 14, and thisresults in an IR drop, AQ/At X R. The resulting IR drop is detected bythe circuit 15 which causes the fuze to function.

The maximum signal for small values of AC is given y v,,, V AC /CApplicant has determined that to a first approximation on a largemunition system that 0 artisan/9 I -I 'f where s is the separationbetween the bodies 11 and 12, and h is the height above the target.

FIG. 2 shows a specific embodiment of the invention constructed inaccordance with the principles described in connection with FIG. 1. Anon-rotating frontal approach munition 20 is provided with thenonradiating, direct current operated fuze of this invention. Twoconducting bodies 21 and 22 are provided which form the forward outersurface of the munition 20, and correspond to 11 and 12 of FIG. 1. Apiece of insulating material 23 serves to separate the bodies 21 and 22while giving mechanical support and maintaining the structural integrityof the munition. The insulating material 23 may, if desired, be allowedto extend beyond the conducting bodies 21 and 22 in order that raindrops in the atmosphere cannot bridge the gap between bodies 21 and 22.Also the area of the conducting bodies 21 and 22 should be made as largeas practicable relative to the edge dimension in order to increase theratio,AC,,/C A direct current supply, corresponding to supply 13 of FIG.1, is provided by a charged capacitor 24 which is charged shortly beforethe projectile is fired. The firing signal is developed across theinternal grid-cathode resistance of the tube 25, corresponding toresistor 14 of FIG. 1, as will be described.

The circuit shown in FIG. 2, including the tube 25 is of the two tube,directly heated hot cathode type, and provides both the functions ofdetecting and triggering. The circuit comprises hot cathode pentode 25with its number 2 grid connected to the conducting body 22 by lead 26and its number 1 grid connected to the positive side of the cathodeforming an accelerating grid for the electrons emitted from the hotcathode. The primary purpose of the pentode 25 is to match the highimpedance of the projectiles proximity signal to the relatively lowimpedance of the trigger tube, thyratron 27. Pentode 25 may also provideamplification.

The plates of pentode 25 and thyratron 27 are connected to a source of Bsupply 28, which may be a charged capacitor 34. A plate load resistor 29is provided for the tube 25. The plate of the tube 25 is also connectedto the control grid 31 of the thyratron 27 through a coupling capacitor32. The control grid 31 is held below below cutoff potential by asuitable negative bias voltage 33. Across the thyratron trigger tube 27are the capacitor 34, a resistor 35 a detonator 36 and an arming switch39. As is well known in the art, when the tube 27 fires, the capacitor34, which at equlibrium had been at the potential of 28, dischargesthrough and actuates the detonator 36 if the switch 39 is closed and theresistance of resistor 35 is sufficiently high.

The supply voltage for the hot cathode supply is provided by a battery37. Additionally, there is provided a setback switch 38 and the armingswitch 39 to make the munition safe for handling and firing in themanner well known in the art.

A short time after the munition is launched, the switches 38 and 39 willclose and equlibrium will be established. At this time, with no targetin close proximity, the signal voltage difference between the number 2grid and the cathode of the pentode 25 will be zero. This will place allthe grids of the pentode 25 at low potential with respect to the cathoderesulting in a small anode current in the anode circuit. Although small,this anode current flowing through the large anode resistor 29 sets theequilibrium voltage at the anode of the tube 25 to a low value. Aspreviously mentioned, the thyratron 27 is held below cutoff by thenegative bias source As a target comes in close proximity to themunition 20 the capacitance between the plates 21 and 22 will increaseappreciably causing a current I =dQ/dt to flow between the number 2 gridand the cathode of pentode 25. The current flow is such as to make thenumber 2 grid negative with respect to the cathode. This causes areduced anode current and a rise in the anode potential, of tube 25which is coupled through the capacitor 32 to grid 31 of the thyratron 27overcoming the negative bias 33 causing the thyratron to fire. Aspreviously described, capacitor 34 discharges through thyratron 27producing a pulse sufficient to actuate detonator 36, and the munitionis exploded.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of the invention as defined in the appended claims.

I claim as my invention:

' 1. A proximity fuze comprising:

a. a first conducting body and a second conducting body, said firstconducting body separated from said second conducting body, said firstand second conducting bodies lying substantially in an edgewise relationon the outer surface of a projectile,

b. a source of direct current potential connected between said firstconducting body and said second conducting body, said source of directcurrent potential establishing an electric field between said bodieswith a positive charge on said first conducting body and a negativecharge on said second conducting body, said electric field extendinginto the medium surrounding said conducting bodies and said projectile,

c. detonating circuit means including vacuum tube means having an anode,a cathode, and a grid, said first conducting body connected to saidgrid, and said second conducting body connected to said cathode, saiddetonating circuit means being responsive to a time rate of change inthe charge on said bodies resulting from a change in the electric fieldconfiguration surrounding said conducting bodies and said projectile.

1. A proximity fuze comprising: a. a first conducting body and a secondconducting body, said first conducting body separated from said secondconducting body, said first and second conducting bodies lyingsubstantially in an edgewise relation on the outer surface of aprojectile, b. a source of direct current potential connected betweensaid first conducting body and said second conducting Body, said sourceof direct current potential establishing an electric field between saidbodies with a positive charge on said first conducting body and anegative charge on said second conducting body, said electric fieldextending into the medium surrounding said conducting bodies and saidprojectile, c. detonating circuit means including vacuum tube meanshaving an anode, a cathode, and a grid, said first conducting bodyconnected to said grid, and said second conducting body connected tosaid cathode, said detonating circuit means being responsive to a timerate of change in the charge on said bodies resulting from a change inthe electric field configuration surrounding said conducting bodies andsaid projectile.